1. Field of the Invention
This invention relates to an injection nozzle on the head portion of an injection machine used for molding by use of a resin.
2. Background Art
An injection molding is performed either by a method by which the injection molding is continued with a nozzle head of a injection nozzle left abutted against a mold, or by a method by which abutting/deabutting of the nozzle head is repeated for each shot. The molding performed by repeating the abutting/deabutting causes a resin stringing to occur by a material resin.
The stringing refers to a phenomenon that when the injection molding is finished and a resin in a sprue bush cools to solidify, the remaining resin in a nozzle bore of the injection nozzle is still in a melted state and thus communicates with the resin remaining in the sprue bush, with the result that as the nozzle leaves the sprue bush, the remaining resin in the nozzle bore is drawn due to the viscous ductility of the resin itself and elongates like string.
The stringing is apt to occur in resins such as polyamide, ABS and polycarbonate, and although a material loss due to the stringing for each shot is not so large, the stringing resin sticks to the periphery of the sprue bush in the mold to cause fouling or a nozzle touch trouble, and a cold stringing resin becomes a cold slug to full up a pin gate or to cause a poor molding (jetting), so that it is desirable to develop stringing preventive means.